allow path and terraform in self-block eval

We can insert the terraform and path values into EvalSelfBlock, since
these are static and always known during evaluation.

lang/eval.go

@@ -72,8 +72,13 @@ func (s *Scope) EvalBlock(body hcl.Body, schema *configschema.Block) (cty.Value,
 
 // EvalSelfBlock evaluates the given body only within the scope of the provided
 // object and instance key data. References to the object must use self, and the
-// key data will only contain count.index or each.key.
+// key data will only contain count.index or each.key. The static values for
+// terraform and path will also be available in this context.
 func (s *Scope) EvalSelfBlock(body hcl.Body, self cty.Value, schema *configschema.Block, keyData instances.RepetitionData) (cty.Value, tfdiags.Diagnostics) {
+	var diags tfdiags.Diagnostics
+
+	spec := schema.DecoderSpec()
+
 	vals := make(map[string]cty.Value)
 	vals["self"] = self
 
@@ -88,12 +93,55 @@ func (s *Scope) EvalSelfBlock(body hcl.Body, self cty.Value, schema *configschem
 		})
 	}
 
+	refs, refDiags := References(hcldec.Variables(body, spec))
+	diags = diags.Append(refDiags)
+
+	terraformAttrs := map[string]cty.Value{}
+	pathAttrs := map[string]cty.Value{}
+
+	// We could always load the static values for Path and Terraform values,
+	// but we want to parse the references so that we can get source ranges for
+	// user diagnostics.
+	for _, ref := range refs {
+		// we already loaded the self value
+		if ref.Subject == addrs.Self {
+			continue
+		}
+
+		switch subj := ref.Subject.(type) {
+		case addrs.PathAttr:
+			val, valDiags := normalizeRefValue(s.Data.GetPathAttr(subj, ref.SourceRange))
+			diags = diags.Append(valDiags)
+			pathAttrs[subj.Name] = val
+
+		case addrs.TerraformAttr:
+			val, valDiags := normalizeRefValue(s.Data.GetTerraformAttr(subj, ref.SourceRange))
+			diags = diags.Append(valDiags)
+			terraformAttrs[subj.Name] = val
+
+		case addrs.CountAttr, addrs.ForEachAttr:
+			// each and count have already been handled.
+
+		default:
+			// This should have been caught in validation, but point the user
+			// to the correct location in case something slipped through.
+			diags = diags.Append(&hcl.Diagnostic{
+				Severity: hcl.DiagError,
+				Summary:  `Invalid reference`,
+				Detail:   fmt.Sprintf("The reference to %q is not valid in this context", ref.Subject),
+				Subject:  ref.SourceRange.ToHCL().Ptr(),
+			})
+		}
+	}
+
+	vals["path"] = cty.ObjectVal(pathAttrs)
+	vals["terraform"] = cty.ObjectVal(terraformAttrs)
+
 	ctx := &hcl.EvalContext{
 		Variables: vals,
 		Functions: s.Functions(),
 	}
 
-	var diags tfdiags.Diagnostics
 	val, decDiags := hcldec.Decode(body, schema.DecoderSpec(), ctx)
 	diags = diags.Append(decDiags)
 	return val, diags

lang/eval_test.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/configs/configschema"
+	"github.com/hashicorp/terraform/instances"
 
 	"github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/hcl/v2/hclsyntax"
@@ -642,3 +643,128 @@ func formattedJSONValue(val cty.Value) string {
 	json.Indent(&buf, j, "", "  ")
 	return buf.String()
 }
+
+func TestScopeEvalSelfBlock(t *testing.T) {
+	data := &dataForTests{
+		PathAttrs: map[string]cty.Value{
+			"module": cty.StringVal("foo/bar"),
+			"cwd":    cty.StringVal("/home/foo/bar"),
+			"root":   cty.StringVal("/home/foo"),
+		},
+		TerraformAttrs: map[string]cty.Value{
+			"workspace": cty.StringVal("default"),
+		},
+	}
+	schema := &configschema.Block{
+		Attributes: map[string]*configschema.Attribute{
+			"attr": {
+				Type: cty.String,
+			},
+			"num": {
+				Type: cty.Number,
+			},
+		},
+	}
+
+	tests := []struct {
+		Config  string
+		Self    cty.Value
+		KeyData instances.RepetitionData
+		Want    map[string]cty.Value
+	}{
+		{
+			Config: `attr = self.foo`,
+			Self: cty.ObjectVal(map[string]cty.Value{
+				"foo": cty.StringVal("bar"),
+			}),
+			KeyData: instances.RepetitionData{
+				CountIndex: cty.NumberIntVal(0),
+			},
+			Want: map[string]cty.Value{
+				"attr": cty.StringVal("bar"),
+				"num":  cty.NullVal(cty.Number),
+			},
+		},
+		{
+			Config: `num = count.index`,
+			KeyData: instances.RepetitionData{
+				CountIndex: cty.NumberIntVal(0),
+			},
+			Want: map[string]cty.Value{
+				"attr": cty.NullVal(cty.String),
+				"num":  cty.NumberIntVal(0),
+			},
+		},
+		{
+			Config: `attr = each.key`,
+			KeyData: instances.RepetitionData{
+				EachKey: cty.StringVal("a"),
+			},
+			Want: map[string]cty.Value{
+				"attr": cty.StringVal("a"),
+				"num":  cty.NullVal(cty.Number),
+			},
+		},
+		{
+			Config: `attr = path.cwd`,
+			Want: map[string]cty.Value{
+				"attr": cty.StringVal("/home/foo/bar"),
+				"num":  cty.NullVal(cty.Number),
+			},
+		},
+		{
+			Config: `attr = path.module`,
+			Want: map[string]cty.Value{
+				"attr": cty.StringVal("foo/bar"),
+				"num":  cty.NullVal(cty.Number),
+			},
+		},
+		{
+			Config: `attr = path.root`,
+			Want: map[string]cty.Value{
+				"attr": cty.StringVal("/home/foo"),
+				"num":  cty.NullVal(cty.Number),
+			},
+		},
+		{
+			Config: `attr = terraform.workspace`,
+			Want: map[string]cty.Value{
+				"attr": cty.StringVal("default"),
+				"num":  cty.NullVal(cty.Number),
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.Config, func(t *testing.T) {
+			file, parseDiags := hclsyntax.ParseConfig([]byte(test.Config), "", hcl.Pos{Line: 1, Column: 1})
+			if len(parseDiags) != 0 {
+				t.Errorf("unexpected diagnostics during parse")
+				for _, diag := range parseDiags {
+					t.Errorf("- %s", diag)
+				}
+				return
+			}
+
+			body := file.Body
+
+			scope := &Scope{
+				Data: data,
+			}
+
+			gotVal, ctxDiags := scope.EvalSelfBlock(body, test.Self, schema, test.KeyData)
+			if ctxDiags.HasErrors() {
+				t.Fatal(ctxDiags.Err())
+			}
+
+			wantVal := cty.ObjectVal(test.Want)
+
+			if !gotVal.RawEquals(wantVal) {
+				t.Errorf(
+					"wrong result\nexpr: %s\ngot:  %#v\nwant: %#v",
+					test.Config, gotVal, wantVal,
+				)
+			}
+		})
+	}
+}